Proteins play significant roles in a human body as a regulatory factor that mediates physiological functions. Mechanism by which proteins interact with biological molecules including proteins, DNA, and/or RNA is pivotal to understand their functions that are regulated by multivalent bindings between heterologous or homologous proteins. Multivalent bindings of protein in a body may perform the following functions of:
(1) generating (e.g., thrombogenesis and actin polymerization) a structure by a protein polymerization,
(2) transmitting signals inside a cell by forming a dimer or multimer through binding of a ligand (glyco)protein to a (glyco)protein between heterologous or homologous membrane proteins, and
(3) expressing a gene through an interaction and binding between intracellular proteins.
As described above, a significant biomodulation, such as thrombus formation in vivo, cancerization and an immune reaction, may occur due to multivalent bindings between proteins in vivo. Accordingly, the multivalent bindings between the proteins in human body need to be detected and analyzed. To detect multivalent bindings of the proteins, a pretreatment process, such as fluorescent labeling, is required in addition to purification of proteins. When such a series of pretreatment processes is not performed, i.e., label-free, it is very difficult to detect multivalent bindings between target protein and binding mediator distinguishably from monovalent bindings. For example, even when a refractive index transducer technology according to conventional arts is used, it is difficult for the refractive index transducer to provide sensitivity enough to detect multivalent bindings and to selectively distinguish multivalent bindings from monovalent bindings.